You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query-continue>
    <backlinks blcontinue="0|Main_Page|18" />
  </query-continue>
  <query>
    <backlinks>
      <bl pageid="3" ns="0" title="Technology level 0" />
      <bl pageid="4" ns="0" title="Technology level I" />
      <bl pageid="5" ns="0" title="In-solvent gem-gum technology" />
      <bl pageid="6" ns="0" title="Gem-gum technology" />
      <bl pageid="7" ns="0" title="Fractal growth speedup limit" />
      <bl pageid="11" ns="0" title="Motor-muscle" />
      <bl pageid="13" ns="0" title="Energy storage cell" />
      <bl pageid="14" ns="0" title="Infinitesimal bearing" />
      <bl pageid="15" ns="0" title="Convergent mechanical actuation" />
      <bl pageid="16" ns="0" title="Community portal" />
    </backlinks>
  </query>
</api>